This invention is related in general to actuators. More specifically, embodiments of the present invention relate to piezoelectric actuators.
Piezoelectric actuators are employed in various demanding applications including robotic flying insects, miniature optical switches, inkjet printers, and micropumps. Such applications demand miniature actuators that can reliably produce relatively large displacements under high dynamic loads.
Piezoelectric actuators are often constructed from dielectric ceramic single crystal or amorphous polycrystalline ceramics, which expand or contract in response to an applied electric field. Unfortunately, conventional piezoelectric ceramics exhibit problematic surface defects resulting from ceramic crystal growth and subsequent processing. Processing may involve cutting piezoelectric materials via a diamond saw or laser. Both cutting methods yield undesirably rough surfaces with relatively large cracks that weaken the piezoelectric materials.
Inherent surface and edge defects in conventional ceramic piezoelectric materials often significantly reduce actuator fracture toughness and fatigue life. Furthermore, such defects cause material stress concentrations, which limit usable working stress range and thereby lower actuator energy density, i.e., work-performing capability per unit mass. Accordingly, actuator operating range is confined to avoid device fracture.
To reduce average crack size, piezoelectric materials are often polished. However, conventional polishing techniques may yield a surface layer of incomplete grains that may actually weaken the piezoelectric material.